The present invention relates to an electrolyzer for extracting a substance from an electrolytic bath. It more particularly applies to the production fo alkaline metals such as lithium, sodium and potassium or alkaline earth metals such as beryllium, magnesium, calcium, strontium and barium, e.g. from the chlorides of these metals.
An electrolyzer is already known which makes it possible to produce lithium from an electrolytic bath containing lithium chloride. This known electrolyzer, diagrammatically shown in FIG. 1a, essentially comprises in the electrolyzer body 2 for filling with the electrolytic bath 3, an anode 4, a metal cathode 6 surrounding the anode, a metal collector 8 in the form of an inverted trough or channel, surmounting the upper end of the cathode and a metal diaphragm 10 which, placed between anode and cathode, is electrically insulated therefrom and extends downwards from the inner edge of the trough 8. The function of this diaphragm is to prevent the cathode-formed lithium from being entrained by the convection currents of the bath outside the space defined by the diaphragm, the cathode and collector 8.
A duct 12 forming an overflow passes through body 2 and issues in the trough permitting the evacuation of the lithium formed by electrolysis and accumulated in said trough (because its density is lower than that of the electrolytic bath. An outlet 14 for the chlorine formed during electrolysis is provided in the upper part of body 2 and a duct issuing into said body 2 in the upper part thereof is provided for introducing an inert gas, such as agron or lithium, into body 2 for preventing the recombination of the chlorine and the lithium and for permitting the discharge of the chlorine as a result of an appropriate inert gas pressure.
The electrolyzer of FIG. 1a can also have (FIG. 1b) an auxiliary anode 18 for polarizing the diaphragm 10 with respect to the electrolytic bath, so as to reduce corrosion of the diaphragm and collector 8, which are raised to the same potential.
The known electrolyzer described hereinbefore suffers from the disadvantage that the diaphragm 10 and cathode 6 are very frequently short circuited during electrolysis by the thrust on the cathode of lithium dendrites which end up by reaching the diaphragm. The lithium then forms on the latter and under these conditions it is at the same potential as the cathode. Therefore the lithium can become detached from the diaphragm in the space defined by the latter and the anode and can reach the electrolytic bath surface, where it partly recombines with the chlorine.